I'm stumped, whats the missing number (1 Viewer)

[Bill Griffith]

Find the missing number in the following sequence.

This problem was given on a 4rth grade math test.

1,5,10,15,25,50,?

I haven't been able to figure it out yet. Not only do you have to say the number but you have to say how you got it.

 

[Lee L]

That is a tough one. At first glance I thought 75 since for all the numbers in the series except the first a+b=c, b+c=d... 5+10+15, 10+15=25, 15+25=50, 25+50=75? but that darn 1 in there has me stumped. We should just eliminate that from consideration sice it doesn't fit the theory.

 

[Brian Perry]

15+25=50

???


I will go out on a limb and say there is a mistake in the original sequence.

(And I will feel stupid if there is a real answer!)

 

[MickeS]

Those have to be some smart 4th graders.

/Mike

 

[Jay H]

Yeah, I was thinking the same thing, until I got to 15+25...

Jay

 

[TimDoss]

Taken from fourth grade test...

2.4 Understand the concept of percent(1%, 5%, 10%, 15%, 25%, 50%, 100%)

coincidence?

 

[TimDoss]

I like this one:

12, 6, 3, 5, ?

 

[MickeS]

So there is no logic, just a random set of numbers that was put down as an example of percentage numbers? That makes more sense... not.

/Mike

 

[Dheiner]

Um, when was the test dated?

 

[MarkHastings]

At first glance I thought 75 since for all the numbers in the series except the first a+b=c, b+c=d... 5+10+15, 10+15=25, 15+25=50, 25+50=75? but that darn 1 in there has me stumped. We should just eliminate that from consideration sice it doesn't fit the theory.

15+25=50???? it actually equals 40.
EDIT - I see Brian already pointed that out...

I want to say it has something to do with currency (i.e. Penny, Nickel, Dime, etc.), but I doubt it.

 

[Graeme Clark]

I don't know about you, but we don't have 15 cent coins around here anyway.

 

[MarkHastings]

I don't know about you, but we don't have 15 cent coins around here anyway.

Well, it might be foreign currency. I guess it would depend on where the test comes from.

 

[Bill Griffith]

Houston fourth grade class, the test was given yesterday.

If the 50 is changed to a 40 it works out nicely at 65. So that was my guess, I think the teacher goofed.

I have a whole room of engineers trying to figure this thing out and no luck yet. We're gonna feel awfully stupid if there is an actual answer to this one.

 

[Ricky Hustle]

The answer is 100, although I'm surprised that question was aimed at 4th graders. My chart is way too sloppy and big to translate onto this page, but eventually patterns emerge when you relate all the numbers together.

 

[Artur Meinild]

12, 6, 3, 5, ?

 

[Bill Griffith]

Rick - yeah, uh ok.

 

[BrianW]

Artur, if your solution were correct, then subsequent numbers would be odd (and incremented by 2) forevermore. It may still be the correct solution, but without a second precedent for treatment of odd numbers, the problem amounts to a despicable fake-out since it suddenly changes the rules on the fourth number.

So I believe that something more consistent must be involved here.

 

[Artur Meinild]

double post... now we don't need two copies of jack black's ass right after each other, do we?

 

[ken thompson]

4 is the missing number

 

[TimDoss]

ken is correct.there are six letters in twelve, three letters in six, five letters in three, and four letters in five